Wood burning stoves, so named because wood is the principal fuel used with them, have existed for many years. Most such stoves are of generally rectangular box-like shape and are fabricated from iron, steel plate or another metal. Common to virtually all wood burning stoves are a combustion chamber or fire box in which the wood is placed for burning; draft inlet means to admit air to the fire chamber for combustion of the wood; and a flue or smokestack to allow hot gases and fumes from the fire to escape from the fire chamber. When in use a wood stove provides heat by radiation from the hot metal surfaces to the air of the building spaces where they are located. Most wood stoves rely principally upon radiation for transferring heat into the room they are located. They often tend to have extremely hot outer surfaces, typically 300° F.-350° F.
Stoves are becoming more widely used as sources of heat for homes, cabins, and the like. These stoves burn wood or coal, or the like, as fuel and have many designs for inputting heat to a room or other such enclosures. Stoves have become commonplace in both residential and commercial applications for situations where a fireplace is not feasible or desired. In some instances, wood burning stoves have been inserted into fireplace boxes because stoves heat spaces more efficiently. Most stoves are able to burn for extended periods of time, such as overnight, without refueling or reloading, further enhancing the preference over fireplaces.
A hot raging fire burns more efficiently than a colder smoldering fire. In a smoldering fire a portion of the gases do not reach the required combustion temperature and exit the stove without burning. These gases are wasted fuel and pollutants. It is therefore better to have a smaller hot fire than a big smoldering fire. Hotter gases rise faster up the flue drawing in air quicker supplying the oxygen for combustion of the wood. The airflow patterns during combustion of wood are a principal cause in fuel combustion efficiency. Adequate air circulation is required to supply the necessary amount of oxygen for the chemical oxidation reaction with the wood cellulose. For rapid combustion and greater air circulation is required. With rapid combustion comes greater temperatures.
Combustion efficiency is a valuable part of a stove evaluation for a home, but it is only one part of the evaluation process and cannot be used as the sole reason or justification for purchasing, keeping or replacing existing equipment. If the excess air is carefully controlled, most stoves are capable of performing at high combustion efficiency.
The ultimate thermal efficiency of the stove is determined by dividing the heat output rate of the appliance by the rate of fuel input. During the combustion process, all stoves that operate with the same combustion efficiency will produce the same amount of heat with the same fuel input. The combustion efficiency has no bearing on how well the stove transfers the produced heat to a building space after the combustion process has taken place. Heat exchanger design and its ability to transfer the heat to the room determines how well the heat produced by the combustion process is utilized.
Typically, such stoves described above and other type heating stoves are designed so as to most efficiently generate heat from a supply of wood whenever the combustion chamber is substantially filled to its recommended wood fuel capacity. Stoves are typically given a heating capacity rating in BTU/hr and selected by the home owner or builder so as to provide adequate heating of a house or room during typical winter weather daytime low temperatures for that location. For instance, in central Canada a
100K btu/hr might be selected for a 1,000 square foot home but only a 50K btu/hr rated stove is required in more temperate Seattle Washington to provide the same comfortable inside house temperatures during winter. The combustion chamber sizes of the same type wood stoves having 100K btu/hr rating vs a 50K btu/hr are predictably substantially larger. If a stove having a 100K btu/hr heating capacity rating was installed in the above described Seattle Washington house the operator would seldom if ever have need to put in a quantity of wood equal to the recommended full load. Operation of a wood stove at less than its recommended full capacity results in the stove operating at a less than optimum thermal efficiency possibly poorer fuel efficiency and possibly poorer stack emissions.
It may just happen to be that such described above house in central Canada one year or more has milder winter temperatures similar to a typical winter in Seattle Washington. The wood stove during such mild winters would only have to be partially filled with respect to its recommended full capacity for wood during the winter and as a result the stove is unnecessarily large and inefficient.
Whenever a combustion chamber is for instance only half filled with wood of its recommended capacity the wood cannot be stacked near as high initially and is proportionally more horizontal than a more fully packed firebox. Cheaper firewood that is typically employed in stoves has its natural circular cross section and as a result has a tendency to roll and is very difficult to stack very highin a freestanding manner on the bottom horizontal surface of stove. Even more expensive split firewood on account of its remaining arcuate surfaces can be difficult to stack in a more vertical manner in a freestanding manner inside the stove. As the half filled sized fire progresses the embers form and fall onto the bottom of the fire box and cover a relatively broader area in comparison to the height of the embers. This relatively flatter pile of resulting embers radiates much of its heat toward the top wall of the stove and even less to the sidewalls, back wall and front door than the original firewood.
Grates for holding wood in fireplaces have been known for many years. Conventional flat grates require constant attention and toil to maintain a warm fire. As the fire burns and the wood is consumed, the contents shift and break apart. The end result is a smoldering fire that has lost its hot nucleus and must be “pushed” back together to maintain. However, the present inventor is not aware of any such type element which improves the efficiency of lesser amounts, such as nearly half the recommended wood capacity, of burning wood more productively.
During milder winters, what is desired is a stove that may operate with substantially lesser amounts of wood at a high thermal efficiency.
The present invention relates to stoves, and, more particularly, to easily adapting a stove to temporarily improve its thermal efficiency during milder winter weather.